Re-Centering the Camera view after Shift Drag?
The only option I know of is to select the camera in question and then press Home before repeating Shift+Numpad Enter

Pressing Home with the camera selected runs the 'View All' command and will bring the camera back in view and centred but it will also adjust the zoom so that all the camera is visible, possibly loosing the 1:1 ratio. So it would be necessary to repeat the 1:1 view shortcut afterwards.